Colonel Mash was born in Hartland, Vermont, on March 11, 1819, and was 44 years of age at the time of his death. He attended Norwich University, a military school in Vermont, where he studied under a well-known officer, Captain Partridge. Later he mover to Ohio, where he studied medicine; after he received his diploma, he returned to Vermont, married, and in 1846, moved with his wife to Potsdam, where he began to practice as a physician. Dr. Marsh was elected to the Board of Trusties of St. Lawrence Academy in 1850, and was a professor of mathematics and natural science there from 1855 until 1859. He was a religious man and a lay preacher in the Methodist Church in Potsdam.

At the battle of Gaines Mill on June 27, 1862, Lt. Col. Marsh received a mortal wound when he was hit by a minie ball, which entered his neck injuring the spinal cord and paralyzing his leg. Marsh was carried from the field by his men and taken to a hospital steamer, where he died a few days later. His body was sent to Fortress Monroe, where it was embalmed and sent home.

"...the citizens of Potsdam in this melancholy event feel that they have met with an irreparable loss and that they mourn with unweigned (sic.) sorrow that premature departure to the spirit world of the beloved physician, the scientific academical teacher, the zealous, pious teacher of the gospel, the true Christian gentleman, and lastly, the brave and gallant soldier, who at his country's call rushed to her defense and sacrificed his life on her alter"